1. Field of the Invention
This invention relates generally to power signal splitters and in particular to active power signal splitters.
2. Related Art
From the inception of convenient cable television (“CATV”) and direct broadcast satellite (“DBS”) services such as those provided by DBS service providers DirectTV® and DISH Network® in the United States and similar services around the world, there has been a tremendous growth in the number of subscribers. As more subscribers enroll for both CATV and DBS services, the CATV and DBS service providers are offering a greater number of services including, but not limited to, additional pay-per view, digital cable transmissions, high definition television (“HDTV”), set-top-box with multiple outputs, broadband Internet, digital music transmissions, satellite radio transmission, personal video recorder (“PVR”), and other bandwidth-intensive services.
Typically, once a subscriber enrolls for either CATV or DBS services, a CATV or DBS service provider connects the subscriber, as shown by the system 100 in FIG. 1, to a CATV (not shown) or DBS network (not shown) via a transmission line 102 (such as a shield-pair transmission line generally known as a “coaxial cable” or optical transmission line such as fiber optic cable) and a satellite 104 communication link 106 utilizing a satellite antenna 108 (such as an active and/or passive array antenna or reflector antenna typically known as a “dish” antenna). The input signals 110 and 112 produced by either the transmission line 102 or satellite antenna 108 are typically input to a set-top box 114 (“STB”) that may be connected to a plurality of output devices including a video monitor 116 (such as a television set), video recorder 118 (such a VCR, DVR, recordable DVD, PVR or other similar type devices) and/or broadband modem 120 of the subscriber. The video monitor 116 may include one or more reception units (such as tuners) such as first tuner 122 and second tuner 124 where the second tuner 124 may be utilized for picture-in-picture (“PIP”) applications. It is appreciated by those skilled in the art that the video monitor 116 may also include the STB 114, video recorder 118 and/or broadband modem 120. It is also appreciated by those skilled in the art that if the STB 114 is integrated into the video monitor 116, the STB 114 may include the first tuner 122 and second tuner 124, and that the STB 114 may also be capable of receiving regular “off the air” television signals (i.e., terrestrial in the case that the transmission line 102 is connected to external “off the air” antenna), CATV and DBS signals, or a combination.
As a result, in both CATV and DBS systems it is desirable to split the input signal (input signal 110 for a CATV system and input signal 112 for a DBS system) for use by more than one portion of the system 100. However, a simple splitting of the input signal into multiple output signal paths without applying gain results in a power loss that is proportional to number of times the input signal is split. Therefore, in order to not degrade the noise performance of the system 100, the splitter (not shown) within the STB 114 should be matched to the impedances of the output devices, have low insertion loss, have low noise-figure (NF), and provide high isolation between all the input and output ports.
In FIG. 2, a prior art example implementation of a system 200 is shown for splitting an input signal 202 from either input signal 110 or input signal 112 shown in FIG. 1. The system 200, FIG. 2, may include a splitter 204 in signal communication with a plurality of reception units of which, for example purposes, four reception units (tuners 206, 208, 210 and 212) are shown connected to the splitter 204 via split signal paths 214, 216, 218 and 220, respectively.
While FIG. 1 showed the STB 114 connected to a plurality of reception units within external devices, it is appreciated by those skilled in the art that as a result of the CATV and DBS service providers (not shown) offering a variety of services to subscribers, a STB for digital and/or analog cable, terrestrial, or satellite reception may typically utilize a multiple number of reception units within the STB. As an example, the tuners 206, FIG. 2, 208, 210 and 212 may produce outputs 222, 224, 226 and 228, respectively, that may be passed to video monitor 116, FIG. 1, video recorder 118 and broadband modem 120, respectively. Therefore, the system 200, FIG. 2, may be either external or internal to the STB 114 of FIG. 1.
Typically, at present the splitter 204, FIG. 2, is usually implemented as a passive splitter utilizing passive elements such as numerous resistors or a set of transformers. As an example, the splitter 204 may be implemented utilizing a Wilkinson divider or cascaded passive network of Wilkinson type. Unfortunately, the use of a passive splitter degrades the overall performance of the tuners 206, 208, 210 and 212 because the passive splitters will cause insertion losses of between approximately 3 to 6 decibels (“dB”) per split, which degrades the performance of the associated tuners by affecting the overall noise figure and signal-to-noise ratio (“SNR”) of the system 200.
In FIG. 3, another prior art example implementation of a system 300 utilizing a low-nose amplifier 302 (“LNA”) for potentially improved performance over the system 100 shown in FIG. 1. The system 300 may include the LNA 302 and a passive splitter 304 in signal communication with a plurality of reception units of which, for example purposes, four reception units (tuners 306, 308, 310 and 312) are shown connected to the splitter 304 via split signal paths 314, 316, 318 and 320, respectively.
Again, it is appreciated by those skilled in the art that the four tuners 306, 308, 310 and 312 may be included within the STB 114, FIG. 1, and may produce outputs 322, FIG. 3, 324, 326 and 328, respectively, that may be passed to video monitor 116, FIG. 1, video recorder 118 and broadband modem 120, respectively.
In this example implementation, the low-noise stage LNA 302 may be placed prior to signal splitting at passive splitter 304. The LNA 302 receives an input signal 330 (from input signals 110, FIG. 1, and 112 produced by either the transmission line 102 or satellite antenna 108) and amplifies and passes it to the passive splitter 304, FIG. 3, via signal path 332. If the LNA 302 has sufficient gain and low noise figure, it may help reduce some of the noise degradation of the system 300 caused by the passive splitter 304.
However, it is appreciated by those skilled in the art that, unfortunately, placing a gain stage, such as LNA 302, before splitting the input signal 330 with passive splitter 304 typically increases implementation complexity and causes poor isolation between the split paths (i.e., the output ports of the passive splitter 304) via split signal paths 314, 316, 318 and 320.
Therefore, there is a need for a system and method that improves upon the performance of current known splitters so that splitting an input signal into multiple split signals does not significantly degrade the overall performance of the system.